This invention was made under the auspices of Bergey Aerospace, Inc. No rights will accrue to any other entity, either governmental, educational, or commercial.
A. Field of the Invention
The present invention relates generally to shock-absorbing structures, more particularly, to safety features incorporated into vehicle seats, namely those found in aircraft, to protect the occupant, insofar as it is possible, from shock induced injury. Such structures find utility in related fields such as automotive, machinery, or any vehicle having human occupants.
B. Description of the Related Art
Designers of vehicles have strived for many years to provide safety devices designed to protect the vehicle occupants from injury in the event of a mishap. Such vehicles include land based vehicles such as automobiles, trucks, earth moving equipment, and the like; sea based vehicles such as boats and submarines; and flying vehicles such as aircraft, helicopters, and spacecraft. All such vehicles feature a to compartment in which the occupants, consisting of the operator and passengers, are seated and surrounded by instrumentation and apparatus for controlling the vehicle. Because the vehicle is generally in motion, external forces may cause the compartment to abruptly change its direction of motion, resulting in forces exerted upon the occupant. If such forces are too great, the occupant can be seriously injured or killed from these forces.
Various means have been proposed to protect the occupant from such forces. Seat belts are a notable example of such protection. They prevent the occupant from being thrown out of the seat and against the instrumentation, control apparatus, or the boundaries of the occupant""s compartment, thus injuring the occupant. However, the seat belt is generally inelastic; that is, when the occupant is abruptly thrown against the seat belt, the force is absorbed by the human body against the seat belt. If the force is too great, then the human body is unable to dissipate the force by its natural elasticity and the tissue or bones will break down, resulting in injury. Some inventors have made an effort to dissipate the force by adding an elastic component to the seat belt which permits the belt to expand somewhat. For example, U.S. Pat. No. 4,060,276, by Maeyerspeer, achieves such elasticity by adding slots in the belt which allow the belt to tear when presented with a specified force to thus absorb the energy of the force.
Other devices protect the occupant by deforming when the occupant is forced against the device. Thus, while seat belts prevent the occupant from being thrown out of the seat, they do nothing to protect the occupant from vertical components of the impact forces such as those commonly experienced in airplane or helicopter accidents. Given that the occupant is in a normal seated position, such forces might be caused by a vertical fall ending in a sudden stop. Cushions, springs, and hydraulic shock absorbers, all installed in the base of the seat, have historically been used to dissipate such sudden and short duration forces. Some of devices exhibit the tendency to return to the original configuration after dissipating the force, resulting in an equal and opposite reaction and allowing the device to resume its shock-absorbing function at a later time.
Le Mire (U.S. Pat. No. 3,586,131) teaches the use of a mechanical energy absorbing device permitting absorbing a thrust by plastic deformation. The device consists of a metal plate having a central fastening point and a plurality of lateral-fastening points. The metal plate has staggered arcuate apertures concentrically arranged around a single centrally-located fastening point so that the plate can expand in tension when subjected to a load tending to move the central fastening point away from at least one of the lateral-fastening points. This device is designed to deform equally in all directions and is thus believed to exhibit isotropic characteristics under load. Le Mire teaches its use for securing or coupling automotive parts likely to be moved or struck by the passengers of a vehicle in case of a violent mishap.
Simpson et. al. (U.S. Pat. No. 5,338,090, Aug. 16, 1994) features a leg structure in a seat frame which deforms to absorb energy. Marechal (U.S. Pat. No. 5,499,783, Mar. 19, 1996) describes device in which energy is dissipated by having a male part which penetrates by force and with plastic deformation into an aperture of a female part, where both parts are components of an underframe for a passenger aircraft seat.
Audi et. al. (U.S. Pat. No. 5,700,545, Dec. 23, 1997) describes an energy absorption device using an expanded metal structure sandwiched between an incident surface and a basal surface, wherein the expanded metal structure is oriented substantially perpendicular to the incident surface. This device is designed so that a force striking an incident surface will cause the expanded metal structure to collapse through plastic deformation during energy absorption so that damage to the object protected by the basal surface is prevented. It is interesting to note that the ends of the strands in this structure are unconstrained, which means that an impacting object deforms the strands in compression rather than in tension, which further facilitates collapse of the structure. The inventors teach the use of this structure for head rests, arresting gear, landing gear, but not for seating arrangements.
Aircraft present unique problems in the design of energy-absorbing structures such as seats. First, weight must be kept to a minimum so that the aircraft may be efficiently operated. Cushions, springs, energy attenuation devices, and hydraulic shock absorbers all have a certain non-trivial and adverse weight and space effects that detract from the utility of the aircraft and other vehicles, thus requiring adverse design tradeoffs that may reduce efficiency of the aircraft. Second, Title 14 of the Code of Federal Regulations, which governs aircraft certification, requires dynamic seat tests, to check the ability of the seat to prevent injury to the occupant when the seat is exposed to associated forces with specified deceleration rates. Cushions, springs, hydraulic shock absorbers, or complex seating frames which deform on impact, most of which operate through compression upon loading, must be substantially constructed in order to provide the necessary protection to the occupant; the resulting construction enhancements and considerations invariably result in increased weight.
Thus, it would be desirable to find an efficient and economical means of seat construction for aircraft and helicopters that will accomplish the following:
1. Support the occupant of an aircraft seat comfortably and without permanent deformation during all normal operations within the approved structural envelope of the aircraft.
2. Absorb energy and thereby attenuate the decelerative forces imposed on the occupant at the deceleration rates and loading angles specified by law and regulation (i.e. the Code of Federal Regulations, Title 14) or in other formal or informal requirements for occupant safety and protection.
3. Exhibit flexibility in configuration so that the point at which plastic deformation occurs can be controlled.
4. Have low weight for aircraft use.
5. Be inexpensive to construct and maintain.
Such considerations as low weight, flexibility in configuration, and energy absorption, and expense would also have utility in seat construction for vehicles other than aircraft and helicopters.
It is therefore an object of the present invention to provide ab energy-absorbing structure which will absorb shock forces experienced by a human being in a seated position within an airborne vehicle.
Another object of the invention is to provide an energy absorbing structure which is light weight.
Another object of the invention is to provide a means of absorbing said shock without the accompanying rebound exhibited by certain conventional energy-absorbing designs.
Another object of the invention is to provide an energy absorbing structure which absorbs forces impacting the structure primarily by means of loading the structure in tension rather than loading the structure in compression.
Another object of the invention is to provide a simple and lightweight energy-absorbing structure which will meet the certification requirements of the United States Federal Aviation Agency as documented in Part 23 of Title 14 of the Code of Federal Regulations or other requirements that may be promulgated by the United States Government from time to time.
Another object of the invention is to provide an energy absorbing structure which is easily constructed from materials well known to the aviation industry.
Another object of the invention is to provide an energy absorbing structure which is relatively inexpensive to build and maintain, as compared with the existing art.
Another object of the invention is to provide an energy absorbing structure which can be supported by a rigid supporting means.
These objects of the invention are achieved by a special seat pan supported by a seating means which provides a space in which the seat pan can expand when subjected to a load normal (i.e., perpendicular) to the incident surface of the seat pan. In the case of an aircraft seat, the seating means provides the structural interface between the seat pan and the cabin structure of the aircraft. The seat pan is formed from a stranded structure which is formed from etched, cast, joined, mechanically perforated, or other forming processes, such structure being formed so as to exhibit nonisotropic characteristics. The best embodiment in this application is an expanded metal structure where the metal has been slit and partially expanded in a manner which will permit the sheet to expand when deformed by a rigid body, namely the body of the occupant when that body is subjected to forces against the seat pan. The slits in the seat pan are designed to deform plastically and permanently under shock loads, so that the seat pan as a unit expands with the force when such loads exceed a given, predetermined limit. This limiting point beyond which plastic deformation occurs is determined by a number of design factors, such as the two-dimensional shape of the seat pan, the manner in which it is supported at its perimeter, the orientation of the apertures in the expanded metal with relationship to the supporting points, the material from which the seat pan is made, and the dimension and shape of the apertures in the seat pan. This plastic deformation will absorb energy and reduce the decelerative forces acting on the occupant of the seat without the reactive component which would tend to return the seat pan to its unexpanded configuration. Such a seat pan is manufactured from light weight materials. Since it replaces a normal component of the seating structure, it does not occupy excessive space or add materially to the weight of the seat structure. The seat pan may optionally be covered with a soft, resilient pad made of such materials as polyurethane, rubber, or cloth materials, in order to increase comfort for the occupant and to more evenly spread the load subjected to the seat pan.
Prior seat designs achieve their energy-absorbing characteristics through plastic deformation of the seat supporting means, whereas the invention described in this disclosure achieves its energy-absorbing characteristics through plastic deformation of the seat pan itself supported by a rigid supporting means. It is believed that this aspect of the invention is unique and novel.